Dehydration of normally gaseous hydrocarbons



Patented Nov. 7, 1944 .Y DEHYDRATION OF NORMALLY GASEOUS HYDROCARBONS Robert Pyzel, New York, N. Y., and Clarence G. Gerhold, Chicago, lll., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application A.any s1, 1941, sei-iai No. 404,890

v4 claims. (cl. 2oz-liz) This invention relates particularly to the dehydration of propane and butanes though the process disclosed may also be applied to dehydration of ethaneor Aheavier vaporizable paralllns. 'I'he present application is a continuation-impart of our copending application ISerial No. 232,571, tiled September 30, 1938.

The invention is more specically concerned with a method for dehydrating butanes which are to be subjected, to dehydrogenation in contact with special types of metal oxide catalysts to pro. duce high yields of the corresponding olefins therefrom. It is in most cases partly essential to keep the water vapor contentof parailinic gas mixtures undergoing catalytic dehydrogenation at a minimum ligure since if appreciable amounts of water vapor are present the life of the catalyst Is adversely affected.

While the olefinic constituents of the gaseous by-products of oil cracking operations are being extensively utilized for the production of addi tional yields of good antiknock gasoline by both thermal and' thermal-catalytic i methods, the utilization of the residual parafiins which are not readily convertible into motor fuel products without the use of extreme conditions of temperature, pressure, and time,'has lagged considerably. 0b viously if eillcient processes are available-for converting gas mixtures such as propane and the butanes into the corresponding mono-oleiins, the utilization oi' cracked gas mixtures and natural gases would be materially simplified and the yield of polymer gasoline or other product would be materially increased. The present process is concerned with means for accomplishing this. end.

In one specific embodiment' the present invention comprises a process for dehydrating paramn hydrocarbons capable of forming constantboil ing azeotropes with water which consists in introducing the water-containing liquid hydrocarbon to a settling zone in which water is separated and removed, subjecting the supernatant hydrocarbon liquid to distillation to produce overhead vapors containing proportionately more water than the residual liquid from the fractionation,

condensing the vapor mixture in the fractionating zone and introducing the condensed hydrocarbons and water to the settling zone, and recovering dehydrated hydrocarbon from the fractionating zone. i

The outline of the process as given in the preceding paragraph will be amplified to indicate its important features in greater detail by describing characteristic operations in connection with thev attached diagrammatic drawing which shows vin general side elevation an arrangement of apparatus in which the process may be conducted. The drawing is not to any absolute or relative scale and the design and relative sizes of individual units may be varied within reasonable wide ranges without departing from the scope of the invention.

Referring to the drawing parafiinic hydrocarbons such as for example propane or butane which require preliminary treatment for the removal of sulfur or other compounds deleterious to the dehydrogenating catalyst, may be introduced to the plant through line I containing valve 2 to a circulating pump 3 which discharges through a filled or packed column mixer I leading to settling tank 5. Aqueous treating solutions are introduced through line 8 containing valve 9 to pump Ill which discharges through line I I containing valve I2 into line 6, which constitutes a recirculating line from a settling tank back to *the circulating pump and is controlled lby valve 1. A definite amount of washing solution is ultimately wasted through line I3 and valve Il to make up for the amount introduced through line 8.

The solutions employed for washing the material introduced (which is preferably under sufficient pressure to maintain it in \liquid phase) consists generally of weak aqueous acids or a1- kalis depending upon the nature of the impurities presentv which may later affect the life oi the dehydrogenating catalyst or catalysts used in subsequent processing. Raw paralilnic gases lor fractions thereof frequently contain hydrogen sulfide, mercaptans, ammonia, and amines. Hydrogen sulfide and methyl mercaptan are removable by the use of caustic soda solutions and the alkaline impurities comprising ammonia and amines may be washed out by Water or very weak acids. The .choice of a wash liquid will depend to a large extent on thenature of the impurities in the charge. If desired both acid and alkalinel solutions may be used if beneficial results are obtained.

The treated material from the upper portion of the settling tank passes through line I5 containing valve I6 to a receiver II which has a vent line I 8 containing a valve I8 for the removal A of incidental accumulations of xed gases and a drain 28 containing a valve 2I for the removal of aqueouslayer. Receiver I1 is preferably tilted Y charged, utilizing for this purpose a lower section heating coil 32 which may be heated by exhaust steam introduced through line 28 containing valve 29 and vented through line 30 containing upstream pressure control valve 3I. The principle upon which the dehydrator operates is the distillation of an azeotropic mixture of hydrocarbon and water which contains proportionately more water than that dissolved in the hydrocarbon charged. The mixture of water vapor and hydrocarbon Vapor passes through line 33 containing up-'stream pressure control valve 34 at a presu sure of approxiniately 100 lbs., per square inch (in the case' of butane; higher in'` the case of propane) and is condensed during ypassage through condenser 34' after which the condensed material flows to receiver il, the excess of water over that soluble in the hydrocarbon appearing as a lower layer and being drawn off through the water drain. The maintenance of approximatelyl a 1:1` recycle ratio in the dehydrator is usually sufficient to insure the dehydrationof the charge to a point consistent with the maintenance of the activity of the dehydrogenating catalyst encountered later in the process.

The dehydrated hydrocarbon leaves dehydrator 21 through line 35 containing valve 36, passes through a cooler 31 and follows line 38 to pump 3S which in turn discharges throughpline 40 containing valve 4i to a catalytic'dehydrogenating unit. A catalyst frequently employed genating processes is of a special character which has been found to be highlyefilcient in dehydrogenating paraffin hydrocarbons to produce mono--4 olefins and di-oleiins therefrom. It consists in general oi granular or pilled particles of specially prepared and activated alumina supporting minor proportions of chromium sesquioxide.. For the purposes oi' the present invention the molecular percentage of fchromium sesquioinde referred to alumina is or lower and good results are usually obtainable when employing alumina supporting between 8 and 16% by weight of thechromium oxi de. Catalysts of this character may be prepared,

by adding ammonium chromate or chromic acid to activated alumina granules and then calcining at a moderate temperature to drive of! water or basic radicalsleaving a depositof the trioxide, Crony The trioxide is then reduced in a stream of, hydrogen or other reducing gas until substantially completely reduced tothe sesquloxide, Which is evidently the effective dehydrogenating catalytic material. n

While alumina-chromia catalyst hs been found to be very effective in dehydrogenatlng parafilnic gases, the dehydrogenating .process itself is not necessarily limited to the use of this particular catalyst, but'may employ other composite catalysts such as, for example, those consisting of other inert refractory carriers than alumina supporting other compounds or oxides than chromium sesquioxide which' have a definite and selective dehydrogenating activity.` Asrepresentative of other inert carriers which may be-employe'd may be mentioned magnesium oxide;

certain types of clays, such as those of a bentonite or montmorillonite variety, either`raw or acid treated; fullersearth; flrebrlck; crushed silica; and glauconite'. Other compounds which have in dehydro-c,k

its rarity and high cost. Other elements thecompounds of which, and particularly the oxides. may be employed are the elements in the left hand columns of groups IV and V oi the periodic table, comprising titanium, zirconium, cerium,

hafnium, and thorium, vanadium, columbiurn, and

tantalum. The catalysts which are alternatively utilizable are not exactly equivalentgin their aca tion and are not to be considered as absolute substitutes one for the other. This fact will be more or less apparent to those convcrsant with the practical aspects of catalysis.

The following general example is introduced to indicate the character of the results obtainable in practice of the invention although not with the intention of unduly circumscribing its proper scope.

A n-butane `fraction obtained from cracked gases was charged to thek plant and thoroughly washed with 10 B. caustic soda for the removai of sulphur compounds. This material was then passed through the dehydrating unit as described in connection with the drawing and distilled under a pressure of lbs., per square inch with n bottom temperature of about F., a 1:1 recycle ratio effecting dehydration of the material to less than .08% water by weight.'

The preliminarily treated and dehydrated nore mal butane fraction could then be dehydro- 1. A method tor separating water from a mix@ I ture thereof`with'liqueiled normally gaseous pan' amn hydrocarbons, which comprises introducing the water-containing hydrocarbon liquid toa settling zone and therein separating water from hydrocarbons, removing wethydrocarbon liquid from saidzone and introducing the same to n dehydrating zone, vaporizingv from the liquid in the dehydrating zone a mixture of hydrocarbons and water containing proportionately more water\than the liquid charged to the dehydranng zone, condensing the vapor mixture from the dehydrating zone and introducing the condensed hydrocarbons and watercto the settling zone, and removing dehydrated hydrocarbon liquid from the dehydrating zone. i L

2. In the puriiication of normally gaseous pan aiiln hydrocarbons by treatment thereof in liquid phase with aqueous renning agents, whereby wa ter is commingled with the hydrocarbons, the method of dehydrating the renedliquefied gas which comprises introducing the 'water-containing liquefied gas to asettIing z one and therein separating water from' hydrocarbo, removing proportionately more water than the liquid charged to the dehydrating zone. condensing the vapor mixture from the dehydrating zone and introducing the condensed hydrocarbons and water to the settling zone, and removing dehydrated hydrocarbon liquid from the dehydrating zone.

3. A method'for dehydrating a liquid mixture 2,362,093 I 3 'containing paramn hydrocarbons and water which comprises introducing the water-contaming hydrocarbon liquid to a settling zone and therein separating water from hydrocarbons, removing wet hydrocarbon liquid from said zone and introducing the same to a dehydrating'zone,

vaporizing from the liquid in lthe dehydrating with the hydrocarbons, the method of dehydrating the refined hydrocarbons which comprises introducing the water-containing hydrocarbon liquid to a settling zone and therein separating water from hydrocarbons, removingwet hydrocarbon liquid from said zone and introducing the same to a dehydrating zone, vaporizing from the liquid in the dehydrating zone a mixture of hydrocarbons andvwater containing proportionately more water than the liquid charged to the dehydrating zone, condensing the vapor mixture fromI the dehydrating zone and introducing the condensed hydrocarbons and water to the settling zone, and removing dehydrated hydrocarbon liquid from the dehydrating zone.

ROBERT PYZEL. CLARENCE G. GERHOID. 

